1. Field of the Invention
The present invention relates to an X-ray fluorescence spectrometer for measuring the intensity of secondary X-rays emitted from a sample which has thin films such as, for example, a semiconductor wafer by irradiating the sample with primary X-rays.
2. Description of the Prior Art
Hitherto, a so-called X-ray fluorescence spectrometer has been well known and widely used for measuring the intensity of secondary X-rays such as fluorescent X-rays emitted from elements contained in a sample by irradiating the sample with primary X-rays and for subsequently determining the concentration of each of the elements or thickness of a film in the sample based on the measured intensity. In the practice of the X-ray fluorescence analysis performed with the use of such analyzing apparatus, depending on the type of the sample to be analyzed, appropriate analytical conditions, for example, the component (element) of interest for analysis, secondary X-ray lines to be measured, the atmosphere in which measurement is carried out, and, the number of orders of calibration curves vary. Accordingly, in the conventional X-ray fluorescence spectrometer, an operator of the analyzing apparatus has determined and set appropriate analytical conditions based on his or her experience.
However, with a so-called thin film sample such as, for example, it often occurs in semiconductor wafers, both the thickness and the composition of each of layers of the thin film are analyzed and that the same elements are contained in different layers. Accordingly, selection of the secondary X-ray lines to be measured is not easy for the operator and, once the selection is inappropriate, no accurate analysis is possible any longer.
In view of the foregoing, the present invention has been devised to substantially eliminate the above discussed inconveniences inherent in the conventional X-ray fluorescence spectrometer and is intended to provide an improved X-ray fluorescence spectrometer capable of performing an accurate analysis by facilitating selection of proper secondary X-ray lines to be measured where the sample to be analyzed is a thin film sample.
In order to accomplish the foregoing object of the present invention, in one aspect of the present invention, there is provided an X-ray fluorescence spectrometer for measuring intensities of secondary X-rays emitted from a sample, which includes a single layered thin film or a multi-layered thin film formed independently or on a substrate, by radiating the sample with primary X-rays, which apparatus includes a measuring line evaluating means and a display control means. The measuring line evaluating means is operable to calculate, for each specified secondary X-ray line to be measured, a first theoretical intensity at a specified thickness and a composition of each of layers of the thin film and a second theoretical intensity at the thickness and the composition thereof when the thickness or a concentration has been changed by a predetermined quantity, to calculate a precision of a thickness or a precision of the concentration based on the first and second theoretical intensities, and to determine applicability or inapplicability of an analysis using the specified secondary X-ray line to be measured based on the calculated thickness precision or the calculated concentration precision. The display control means is adapted to cause a display unit to display the applicability or inapplicability of the analysis determined by the measuring line evaluating means.
With the X-ray fluorescence spectrometer of the structure described above, since the applicability or inapplicability of the analysis of the thin film sample with the specified secondary X-ray line to be measured can be displayed, the operator can easily and properly select the proper secondary X-ray lines to be measured and, accordingly, an accurate analysis is possible.
In a preferred embodiment of the present invention, the measuring line evaluating means may determine whether or not the specified secondary X-ray line to be measured can be applied to a calibration curve method depending on a presence or absence of a specification for the analysis of the concentration in the layer where the specified secondary X-ray line to be measured is applied in an analysis of the thickness of the layer based on the calibration curve method, or depending on the presence or absence of the specification of the analysis of the thickness of a layer where the specified secondary X-ray line to be measured is applied to an analysis of the concentration of the layer. The display control means then causes the display unit to provide a visual indication of the applicability or inapplicability to the calibration curve method so determined by the measuring line evaluating means.
According to the above described embodiment, since the applicability or inapplicability of the specified secondary X-ray line to be measured to the calibration curve method is displayed, the operator can, based on the displayed indication, select a proper secondary X-ray lines to be measured easily particularly when the analysis is to be performed with the calibration curve method, so that an accurate analysis can be performed.
In another aspect of the present invention, there is provided an X-ray fluorescence spectrometer for measuring intensities of secondary X-rays emitted from a sample, which is a single layered thin film or a multi-layered thin film formed independently or on a substrate, by irradiating the sample with primary X-rays, which apparatus includes a measuring line evaluating means and a display control means. The measuring line evaluating means is operable to calculate, for each secondary X-ray emitted from the sample, a first theoretical intensity at a specified thickness and the composition of each of the layers of the thin film and a second theoretical intensity at the thickness and the composition thereof when the thickness or the concentration has been changed by a predetermined quantity, to calculate a precision of a thickness or a precision of the concentration based on the first and second theoretical intensities, and to select the secondary X-ray line to be measured based on the calculated thickness precision or the calculated concentration precision along with determination of applicability or inapplicability of the analysis using the secondary X-ray line to be measured so selected. The display control means is adapted to cause a display unit to display the applicability or inapplicability of the analysis determined by the measuring line evaluating means.
With the X-ray fluorescence spectrometer of the structure described above, since with respect to the thin film sample, the secondary X-ray lines to be measured can be automatically and properly selected by the measuring line evaluating means based on the calculated thickness precision or the calculated concentration precision, the operator need not to select the secondary X-ray lines to be measured which is one of the analytical conditions and an accurate analysis can be performed. Moreover, since the applicability or inapplicability of the analysis of the thin film sample with the automatically selected secondary X-ray lines to be measured can be displayed, the operator can easily perform an accurate analysis while avoiding an inaccurate analysis with reference to the display given by the display unit.
In a preferred embodiment of the present invention, the apparatus according to the second mentioned aspect of the present invention may further include a control device for executing an analysis of the sample according to predetermined analytical conditions and wherein the measuring line evaluating means applies the selected secondary X-ray lines to be measured to the control device as a portion of the proper analytical conditions depending on the applicability or inapplicability of the analysis so determined.
Where the control device is employed, the secondary X-ray lines to be measured that have been automatically selected can be automatically set as a part of the proper analytical conditions and, accordingly, the operator can be relieved from a burden of setting the secondary X-ray lines to be measured that form a part of the analytical conditions.
In the apparatus according to any one of the first and second mentioned aspects of the present invention, the measuring line evaluating means may preferably calculate, for each secondary X-ray line, theoretical intensities of a background thereof and then calculates a precision of a thickness or a precision of the concentration using the theoretical intensity of the background and the first and second theoretical intensities.
According to this embodiment, since the measuring line evaluating means calculates the thickness precision or the concentration precision using the theoretical intensity of the background together with the first and second theoretical intensities, determination of the applicability or inapplicability of the analysis with the secondary X-ray line to be measured can be performed more accurately and the operator can perform the accurate analysis based on that.
According to a further aspect of the present invention, there is provided an X-ray fluorescence spectrometer for measuring an intensity of secondary X-rays emitted from a sample, which is a single layered thin film or a multi-layered thin film formed independently or on a substrate, by irradiating the sample with primary X-rays, which apparatus includes a measuring line evaluating means and a display control means. The measuring line evaluating means is operable to calculate, for each specified secondary X-ray line, at a thickness value and a composition specified for each of the layers of the thin film, at least two numerical values from five numerical values including an overall intensity that is a theoretical intensity from the sample in its entirety; a layer intensity that is a theoretical intensity from the substrate or each layer of the thin film; a single layer intensity that is a theoretical intensity exclusive of an absorption of upper layers from the layer intensity; an attenuation ratio that is obtained by dividing the layer intensity by the single layer intensity; a ratio to infinite thickness that is a ratio of the single layer intensity at the specified thickness relative to the single layer intensity when the layer is deemed having an infinite thickness in terms of X-rays, and to select comments from pre-stored comments for the analysis based on the calculated numerical values. The display control means is adapted to cause a display unit to provide an indication of the numerical values and the comments both calculated and selected by the measuring line evaluating means.
With the analyzing apparatus according to the third mentioned aspect of the present invention, since the proper comments for the analysis together with the overall intensity, the layer intensity and others can be displayed by the display unit, the operator looking at the display unit can easily select the proper secondary X-ray lines to be measured and, therefore, can perform an accurate analysis.